Imagine the hypothetical acid HA whose equilibrium is
HnAm (aq) ⇄ nH+ + m A-
And the Ka is, Ka = [H+]^n * [A-]^m / [HnAm]
Aciditiy is a measure of the [H+] in equilibbrium.
The higher [H+] the higher the acidity.
And from the equation
- the higher [H+] the higher Ka,
- the lower [H+] the lower Ka
- the higher Ka the higher [H+].
- the lower Ka the lower [H+]
Then, you conclude that for a low Ka (which 1.6 * 10^-10 is) the acidity is low.
That means that the corresponding acid has a low acidity (it is a weak acid).
You can calculte the acidity as the pKa
pKa = log { 1 / Ka} = log { 1 / ( 1.6*10^-10) } = 9.8
Answer: the acidity is low with a pKa of 9.8.
